PHOENIX (AP) -- Jodi Arias has acknowledged shooting, stabbing and slitting the throat of her lover. She says it was self-defense: Kill or be killed.

Her lawyers began making their self-defense case Tuesday - a daunting task after Arias, now 32, initially denied any involvement in the 2008 death of Travis Alexander, then blamed it on intruders.

Arias' lawyers also must explain to jurors why she brought a gun to a sex tryst, took pictures after Alexander was dead, tried to destroy the camera in a washing machine, and fled.

Legal experts say the primary goal for the defense lawyers might simply be to spare Arias the death penalty.

The first of two defense witnesses who testified Tuesday talked mostly about his business mentoring relationship with Arias and was asked about how provocatively she dressed.

Witness Gus Searcy once worked with Arias at a company that designs, underwrites and markets legal expense plans.

"She was always dressed very feminine, but very conservatively," Searcy testified, noting that he never witnessed Arias acting sexually inappropriate.

Friction erupted between Searcy and prosecutor Juan Martinez when Martinez likened the company's structure to a pyramid where top company officials get a cut of profits earned by people at the bottom.

"It's not a pyramid, so to say it is, is wrong," Searcy said, noting that he never earned a dime from his mentorship of Arias.

Searcy was followed to the witness stand by Daryl Brewer, who dated Arias for four years until 2006. He said Arias had become more involved in the Mormon church.

"She was taking religion more seriously," he said.

Brewer, who remained friends with Arias for several more years, said he never saw her become violent or jealous toward other women. He described Arias as sexually aggressive and said she once took a nude picture of him in the shower.

Lead defense attorney Kirk Nurmi declined to say which witnesses he will call Wednesday.

Arias could become the fourth woman on Arizona's death row if she's convicted of killing Alexander.

Authorities allege that Arias shot Alexander in the face, stabbed and slashed him nearly 30 times, slit his throat and left him inside a shower at his suburban Phoenix home after he tried to end their relationship.

Prosecutors argue Arias went to Alexander's home intent on killing him after learning he planned to take a trip to Mexico with another woman.

Arias claimed she ended their relationship, but the two continued a sexual affair.

Police say Arias' bloody palm print and hair were found at the crime scene, and they found sexually explicit, time-stamped photographs in the camera that placed Arias there on the day of the killing.

Arias told police that on the day of the killing, Alexander invited her to his home for sex then became enraged when she dropped his new camera while snapping photos of him. She claims she had to fight for her life.

The photos show Arias nude in Alexander's home and Alexander alive in the shower, then dead in the bathroom.

Defense lawyers have yet to explain why she put the camera in a washing machine.

Authorities say Alexander was shot with a .25-caliber gun, the same caliber weapon her grandparents reported stolen from their California home just days before the killing. Police have not recovered any of the weapons used in the slaying.